They only ever try this shit for small relatively inconsequential stuff and since most sovereign citizens are middle class people a lot of them do kind of get away with it (not because of the sovereign citizen stuff but because it's small potatoes and the justice system is kinder to middle class people than it is to poor people, so their case/charges often get dropped or dismissed or they get a good deal, etc) and I'm pretty sure that leads them to believing that it does work more often than not and they tell all their friends at the next BBQ about how they totally beat the system with this one neat trick. Like I've never heard of a sovereign citizen trying this shit for stuff like grand theft, assault, murder, etc. It's always stuff like low level traffic violations, which are already things they're likely to only get a slap on the wrist for.